Apparatus for heat interchange



May 22, 1934. H. HOLZWARTH 1,959,362

APPARATUS FOR HEAT INTERCHANGE Filed April 20, 1931 4 Sheets-Sheet 1 Fly. 1.

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APPARATUS FOR HEAT INTERGHANGE Filed April 20,1951 4 Sheets-Sheet '4 Patented May 22, 1934 UNITED STATES APPARATUS FOR HEAT INTERCHANGE Hans Holzwarth, Dusseldorf, Germany, assignor to The Holzwarth Gas Turbine Company, San Francisco, Calif., a corporation of Delaware Application April 20, 1931, Serial No. 531,266 In Germany April 23, 1930 4 Claims. (01. 257--247) My invention relates to heat exchangers and has for its object to provide a novel and improved apparatus for effecting heat interchange between two fluids.

v The present invention proceeds from the observation that the processes anddevices heretofore employed for transferring heat from substances of poor conductivity, as for example highly heated oil, to substances of better heat conductivity, as for example water, are entirely incapable of attaining sufficiently high rates of heat transmission. Thus for example, in the investigations of Heinrich Stueckle (Forschungsheft 2'71) the coefficient of heat transfer from oil through the wall of a tube to water at oil velocities between 0 and 1 meter per second is given as 50 to a maximum of 300 ca1./m /hr/'C.'(large or kilogram calories per square meter of heat transfer surface per hour per degree centigrade) 20 A heat exchanger designed upon the basis of such coefiicients of heat transfer would be extremely bulky and cumbersome and would consequently offer large cooling surfaces from which heat would be lost to the atmosphere, so that an apparatus of this kind is not only expensive, but unsatisfactory from the standpoint of heat economy.

The present invention makes possible a surprising increase in the rate of heat transfer beyond values of about 1600 caL/m /hr/ C., and 30 accomplishes such result by conducting the sub- 7 stance of poor heat conductivity along the heat transferring wall in' the form of a thin film and with an average velocity of at least 1.3m/sec.

The film may be produced in various ways; for example, the tubes traversed by thematerial of poor heat conductivity are provided with cores of such external diameter that there is left only a narrow annular space, through which such substance flows in the form of a hollow cylindrical film; the tubes being at the same time contacted along their outer surfaces by the substance of better heat conductivity. These annular spaces may be created also by placing two concentric tubes one within the other and causing the better heat conducting substance to flow through the interior of the inner tube. The first-mentioned form of the invention has the advantage of much greater simplicity. The annular intermediate space can be subdivided in the manner of a helix. The ribs or other deviceswhich produce the helical subdivision of the intermediate space between the inner wall of the tube and the core insert may advantageously be formed or positioned between suitable notches or depressions in the inner wall of the tube. The ribs may also be arranged upon better heat conductivity, such as water.

the core itself; researches have shown, however, that the formation of the ribs upon the inner wall of the tubes is more advantageous from the standpoint of heat transfer. The tubes may be given any known special construction upon the sides contacted by the better heat conducting material for improving the heat transfer; for example, they may be provided with projections or ribs or similar devices for increasing the heat transfer surfaces. 7

On the accompanying drawings is shown a graph (Fig. 1) on which the coordinates are divided logarithmically, the ordinates representing the rates of heat transfer obtained according to the invention, expressed in cal./m /hr./ C., while the abscissa: represent the average oil velocities in meters per second. The curves represent the results of experiments made with a hollow cylindrical film. With the curve 10. the average oil temperature was 0.; with the curve 11), (3.; with the curve 10, C.; with the curve 1d, 200 C.; with the curve 1e, 225 0.; and with the curve 1], 250 C. The curves show that at oil velocities slightly above 1.3m/sec. a point of instability appears, beyond which a rapid increase in the heat coefiicients is to be observed.

In accordance with the present invention, therefore, oil velocities above 1'.3m/sec. are employed together with the feature that the material of poor heat conductivity is conducted along the heat transferring wall in the form of a thin film, so that the rate of heat transfer can be raised from 4 to about 32 times the value heretofore attainable; the heat transfer surfaces can therefore be reduced to a corresponding extent as compared with the surface areas heretofore required.

If high boiling oils serve'as the material of poor heat conductivity, there arises the unfavorable circumstance that the oil, when the apparatus is not in operation, forms a viscous layer in the narrow spaces available for film formation, which layer cannot be completely removed even by the use of high pressures. In a further development of the invention, certain of the tubes in the heat exchanger are not filled with cores but have their whole interior free for the passage of oil. As soon as the plant is started, these tubes are immediately traversed by the highly heated oil and effect the transfer of heat to the substance of The water becomes heated and in turn heats the thickened oil films which clog the annular spaces in the tubes provided with cores. Under the infiuence of the heating, the viscosity of the oil layer is reduced so that the flow of oil through cored tubes takes place. The tubes not provided with cores are preferably closed at this instant against the entry of oil, by either manually or automatically (e. g. thermostatically) operated devices, so that from this moment on, the heat exchange takes place under the favorable conditions provided by the present invention.

The heat exchangers to be employed in carrying out my improved process may be constructed in various ways. A particularly simple construction results when the tubes provided with core inserts are arranged between two collectorchambers or headers for the uncooled and the cooled substance of poor heat conductivity, inthe manner of the heating tubes of a tubular boiler. Upon removal of the covers of the collector chambers, the core inserts can be comparatively easily removed from the heating tubes connecting such chambers, so that the tubes can be readily cleaned.

The tubes with the core inserts can, however, be connected to collecting chambers, so as to project laterally therefrom in the manner of a cantilever, in which the inserts are provided with bores communicating with such chambers and serving to conduct the substance of poor heat conductivity in one direction to the far end of the tube where the oil reverses in direction and flows through the annular spaces. If these bores are connected with the collecting chambers for the uncooled substance of poor heat conductivity, the advantags is obtained that when a plant is set into operation with the use of oil as the heat carrier, the uncooled hot oil first flows into the hollow spaces in the inserts and thus heats up the viscous oil films clogging the annular spaces about such inserts. Insuch an arrangement it becomes'unnecessary to provide special starting tubes with out inserts. The tubes with the core inserts can be arranged at both sides of the collecting chambers for the uncooled and the cooled substance of poor heat conductivity, so that by displacingv the tubes of adjoining chambers it is possible to combine the tubes into groups and to dispose a number of groups, one behind the other, along the length of the heat exchanger.

Heat exchangers built in accordance withthe present invention are of particular utility for the transfer to water of the heatabstracted by cooling oil from combustion engines, particularly combustion turbines. In the cooling of combustion turbines, the most diverse conditions must be maintained. First of all, the cooling may be driven only to such a degree that, on the one hand, the structural materials are still protected against excessive temperatures, while on the other hand, the efficiency of the power plant is not impaired by an unnecessarily large abstraction of heat. In particular, the cooling process must be so determined that the heat transferred to, the cooling medium can be utilized as completely. and as efliciently as possible 'in the operation of the combustion turbine plant. If, for example, as already proposed, water is employed as the cooling medium, a definite maximum temperature may not be exceeded if the formation of steam is to be avoided with certainty; or else the cooling water must be placed under pressure to avoid the formation of steam. Cooling with liquid water with the maintenance of a definite maximum tempera ture is prejudicial to the over-all efiiciency of the plant because the withdrawn heat cannot be utilized efiiciently; placing the water under pressure has the disadvantage that the cooling jackets must be made pressure proof. To avoid these disadvantages, it has already been proposed to employ high boiling cooling media, as for example high boiling oil as the cooling agent in piston combustion engines. If, however, the cooling oil temperature were permitted to rise sufiiciently high in such piston engines to make possible the generation of steam of an economical pressure, the cylinder wall temperatures would rise so high as to make proper lubrication of the piston exceedingly difiicult, if not extirely impossible. This limitation does not exist in combustion turbines because the parts to be cooled, as for example the walls of the explosion chambers, the nozzles, the nozzle ring and the rotor housing, neither move nor are in contact with moving parts, so that the matter of slidably guiding other machine parts within one of the cooled parts need not be taken into consideration at all. In addition, a special advantage occurs in combustion turbines operating with intermittent regulation in which individual explosion chambers are set into or cut out of operation toincrease or decrease the output of the plant. The carrying out of this method of control requires that as soon as idleexplosion chambers are cut in they must immediately assume normal operating conditions in order that the degree of non-uniformity of the machine may remain within permissible limits. If the idle explosion chambers were permitted to become cold while they were not in operation, the regulation of the plant would be subject to serious difficulties. Because of the fact that the idle explosion chambers are constantly traversed by the hot cooling oil stream, they remain at a temperature which makes immediate starting of such explosion chambers possible.

In addition to securing these advantages as contrasted with the known modes of cooling, my novel cooling process for combustion turbines is distinguished over prior processes also by the fact that the heated cooling oil for absorbing the heat of the parts to be cooled is conducted past water-cooled walls in the forms of a thin film and with an average velocity of at least 1.3 m/sec., and the generated steam then introduced in the heat economy of the combustion turbine, as by being charged into a gas turbine to assist in keeping the blades and other parts thereof cool, or into a steam turbine forming part of the power plant. If for example, the oil is introduced into the combustion turbine at a temperature of 230 C., or if the recooling of the heated oil is made to take place only down to this temperature, and a temperature rise of about 35 is permitted in the cooling jackets, the heated oil is in a condition to generate steam in the heat exchanger of an economical, useful pressure of about 20 atmospheres. This steam pressure is obtained without the necessity of making the cooling jackets of. the combustion turbine proof against this high pressure. Thecooling oil temperature itself can be'raised, without the limita tions present in piston combustion engine operation, to such a height as is necessary for the production of steam of an economical pressure. My improved cooling process thus affords, by the use of intermittent regulation, the particular advantage thatthe temperature conditions in all of the cooling chambers are maintained uniform in spite of the cutting out of certain of the explosion chambers. Steam generators constructed according to the present invention oifer particular advantages in combustion-engine power plantsyespecially constant volume explosion turbine plants for ve-.

hicles, preferably locomotives, such as described in my copending application Serial-No. 512,340, because the space requirement of'my improved heat exchangers is so small that they maybe positioned, for example, upon the roof of the vehicle and thus do not interfere with the machine structures themselves, and enable the pre-' scribed profilefor the locomotive to be maintained. 1 1 v The accompanying drawings illustrate by way of example two embodiments of the invention; in

said drawings, w

Fig. 1 presents a'graph showing the relationship between the rate of heat transfer andthe average velocity of the oil;

Fig. 2 is a vertical longitudinal section of a heat exchanger built in accordance with the present invention; 1

Figs. 3 and4 are transverse sections along the lines IIIIII and IV-IV of Fig. 2;

Fig. 5 illustrates a second embodiment of the invention; 1 f l Fig. 6'shows on an enlarged scalealongitudinal section through the groups of connections ofadjoining collecting chambers; and

Figs. 7, 8 and 9 are transversevcrtical sections along the lines VII-VII, VIII-VIII and IXIX respectively, of Fig. 5. I

The numeral 5 designates the boiler in whic the heat of the cooling oil is transferred to liquid, preferably preheated water to generate steam therefrom. The feed water flows through conduit 6 first into the distributing space 7 and from the latter it is introduced into the boiler space 35 M cores 10 which leave intervening annular spaces til I for starting the apparatus.

T viscosity of such oil films.

of such radial depth as to form the oil streams flowing through the tubes into thin unbroken cylindrical films. The cores are centered in the tubes 10 in any suitable manner (not shown);

for this purpose, centering ribs may, for example, be provided on the inner surfaces of the tubes,

or the ends of the tubes may be provided with bushings which support the ends of the inserts.

As is shown in Fig. 3, separate tubes 16 are provided which have no core inserts and serve On starting, when the congealed or highly viscous oil films in the cored tubes move very sluggishly or not at all, the tubes 16 are traversed by the heating oil without difficulty as they oppose less resistance to the latter so that the body of water in the boiler 5 becomes heated and in turn heats the congealed oil films located in the annular spaces between the cores 15 and the inner walls of the heating tubes 10 and thereby reduces the After a short time, the viscosity of the oil films is reduced to such an extent that they begin to flow rapidly and thus the conditions for oil film formation according to the invention are fulfilled. At about this instant, the tubes 16 are closed by any suitable devices, as by means of plugs 16a located within one of the headers and operable from the exterior thereof with the aid of a rack 16b and a manually movable gear segment 160, or

i by means of a valve-controlled conduit leading th'ereint'ojso that underv the influence of the high rate of heat interchange secured by the present invention, such rateamounting up to about. 1600 cal./m /hour/ 0., rapid steam generation sets in. The steam generated is withdrawn bypipe 17 and conducted to a place of use. vA modified construction according to the invention'is shown in Figs. 5 to 9. As is shown in Fig. 6, only short connecting pipes are employedfor the heattransfer from the hotv oil to the water- These pipes consist of cores 19 provided with bores 18, such cores filling the heating tubes 20 to such an extent as to leave only narrow annular spaces 21. These spaces 21are divided into spiral pathsby means of ribs 22 on theinner surfaces of the tubes 20 and are connected on the one hand at the ends of thetubes with the bores 18 of the inserts 19, and on the other hand they are connected at the 'beginning'of the tubes with the collecting chambers 23 for the cooled heating 'oil. The chambers 23 for the cooled oil form the jacket of the collecting chamber 24 for the uncooled oil. The walls 25 of the collecting chamber124 carry the core inserts 19 by means of threaded connections 26, While the jacket walls 27 forming the jacket space 23 for collecting and conducting the cooled oil serve to support the heating tubes 20 in cantilever fashion. The uncooled, oil thus flows first through the bores 18 of the core inserts 19 and thereby, on starting of the oil boiler, reduces the viscosity of the oil films in the narrow spiral passageways 21. After a short time, the hot oil infiltrates into the spaces 21 in the form of a thin film, after which the method of heat transfer according to the invention comes into operation. The feed water in space 28 outside of the heating tubes 20 is then rapidly heated to boiling and the generated steam is withdrawn through pipe 17.

As is shown in Fig. 5, each of the collecting chambers except the end chambers of the heat exchanger carries heating tubes 20 at both sides thereof, the tubes being so disposed that between each two chambers agroup of heating tubes for each chamber is arranged, and in this way a maximum of heat transfer surface is created. The heating tubes 26 may be provided upon their external surfaces with any known means 29 for increasing their heat transfer area. The collecting chamber 24 for the uncooled oil is connected with a supply tube 30 (see Figs. '7 to 9) while jacket space 23 for the cooled oil is connected with a discharge conduit 31. If a heat exchanger built in accordance with the invention is employed to utilize the heat abstracted by the cooling oil in the cooling jackets of a combustion gas turbine by generating steam with such heat, the conduit 30 is connected with discharge con nections of the cooling jackets of such combustion turbine, while the conduit 31 leads to the inlet connections of the turbine for the cooled oil. In the same manner as already described in connection with Fig. 2, the feed water is conducted into the distributing chamber 33 by pipe 32 and is conducted from the latter by tubes 34, 35 or 36, 3'7 distributed along the length of the boiler.

It will be understood that other heat transferring media may be employed besides oil; and that my improved heat exchanger may be employed for the generation of steam or for the evaporation of liquids by indirect heating.

I claim:

1. A heat exchanger comprising a plurality of tubes having core inserts therein of such diameter as to form narrow annular spaces between the inner walls of the tubes and the outer surfaces of such cores, means for conducting a substance of poor heat conductivity into said annular spaces, means for conducting a substance of better heat conductivity against the outer walls of the tubes, and tubes not provided with cores for use in starting the apparatus. 7

2. A heat exchanger comprising a plurality of tubes having core inserts therein of such diameter as to form narrow annular spaces between the inner walls of the tubes and the outer surfaces of such cores, means for conducting a substance of poor heat conductivity into said annular spaces, means for conducting a substance of better heat conductivity against the outer walls of the tubes, said exchanger including tubes not provided with cores for use in starting the apparatus, and means for closing such last-mentioned tubes against the entry of the substance of poor heat conductivity after the apparatus has been started.

3. A heat exchanger comprising a plurality of tubes having core inserts therein of such diameter as to form narrow annular spaces between the innerwalls of the tubes and the outer surfaces of such cores, means for conducting a substance of poor heat conductivity into said annular spaces, means for conducting a substance of better heat conductivity against the outer wallsof the tubes,

msascz collecting chambers for the uncooled and the cooled substance of poorheat conductivity, said tubes arranged at both sides of the chambers and connected into, groups, a plurality of such groups with their associated chambers being disposed along the length of the heat exchanger one behind the other.

4. A heat exchanger comprising a plurality of tubes having hollow core inserts therein of such external diameter as to form narrow annular spaces betweenthe inner walls of the tubes and the outer surfaces of such cores, the outer ends of said cores being open and communicating with said annular spaces, and the outer ends of said tubes being closed, a collecting, chamber connected with the inner ends of said cores and communicating with the interior thereof, a conduit for conducting a fluid into said chamber for distribution into said cores and thence into said annular spaces, a second collecting chamber connected with said tubes to support the latter in cantilever fashion and receiving the said fluid after the same has traversed said annular spaces, means for withdrawing the fluid from said second chamber, and means for directing a second fluid against the outer surfaces of said tubes and into heat exchange, relation with the first-mentioned fluid.

HANS HOLZWARTH. 

